Conventional semiconductor devices used in power equipment have been known that solder cracks occur because heat generated when current flows through power semiconductor elements is applied as thermal stress to the power semiconductor elements, and thus stress is applied to solder portions provided on lower surfaces of the power semiconductor elements.
Progress of the solder cracks increases a heat resistance of the power semiconductor elements that exceeds the limits of heat resistance, possibly leading to breakage of the power semiconductor elements.
Patent Document 1 discloses as follows. A heat resistance of a power semiconductor element during on-off control is obtained by a computation, the product life of the power semiconductor element is determined on the basis of the obtained heat resistance, and a collector current value is controlled to be limited as necessary.